Beomaster 3000-2 Type 2402 15V Power Supply Not Activating

[Johnny Law]

Hi All –

This is a cross-post from AudioKarma (thread here) but I am hoping folks here may have more experience with this …

Basically, in my 3000-2, the 15V power supply is not activating unless I touch TR17B or TR17C with something metal.

Once I do that and it switches on, the 15V power supply works great and I can listen to music (via Tape input) no problem.

The unit has all new electrolytic capacitors including the main PS cap and both output caps, and new rectifiers.  I’ve confirmed every single component in the 15V PS circuit is operational.  I’ve also de-oxited all the pots that are fed by the 15V PS.

Through a DBT, the below in yellow are the values before it starts conducting, but after I touch TR17B or TR17C and switches on, then the green values appear and all is good.

Any ideas as to why TR17 doesn’t start conducting on its own when the unit is powered on?

Scratching my head over here.  Appreciate any tips, suggestions, follow-up questions … thank you!

[hcraig244]

Replace ZF9,1V……..see if that helps, if not then at least you can eliminate it from the problem

Craig

[Johnny Law]

Craig: Thank you!

I should have noted the work done … everything in green boxes in my graphic (aka, every component in the circuit) has been replaced and/or tested OK.

I see the same behavior either with the original 9.1V zener or with a new replacement 9.1V zener (specifically, a NZX9V1D).

The issue (I think) is that for some reason there’s no current through R150 & R151 to create the voltage drop needed at TR17’s base, which once activated would flow current through R146 to activate ZD148.

Despite weeks of scratching my head and trying different things, I can’t determine why that’s the case …

One idea was that the 15V PS load is too small – I confirmed in LTSpice that if the load is 1ohm, the PS won’t engage.

But, I measured the resistance from the +15V PS to ground and am seeing 285ohms.  Modeling that effective startup resistance in LTSpice, the power supply should still activate.

 

(I’d post the LTSpice images, but I’m new to the forum and it won’t let me either copy / paste images, upload them in the image upload tool, or attach them as files for some reason?  Is the image tool operational on this forum?)

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